The invention relates to coal-burning utility electrical power generation plants, and more particularly to a mill head access door.
In a coal-burning utility electrical power generation plant, a ball tube mill is provided for pulverizing the coal. The mill includes a drum rotational about an axis and having mill heads at distally opposite axial ends thereof. Stationary dividing plates divide each respective mill head into an entrance receiving coal, and an exit discharging pulverized coal dust. Openable doors on the mill heads allow access by maintenance personnel, including scheduled removal and replacement of the respective divider plate.
The work performed in the mill is particularly difficult. It is performed in a confined space, and requires precautionary measures to protect personnel prior to entry into the mill. The atmosphere is hot and dirty, especially because of the coal dust. Some areas of the mill are very small and quite uncomfortable to work in for the majority of individuals. Some of the parts within the mill to be replaced are large and require mechanical lifting equipment to install, and in some cases require sizing or cutting to fit through the door opening. The noted divider plate must be cut, for example, by an acetylene torch into four or more pieces, to fit through the door opening. In the replacement of mill liners, the mill end has to be cut in order to gain access to do the work.
To solve the above noted problems, a new modified design has been developed to allow better access to the mill for personnel and equipment for numerous tasks, including repair of the inlet side of the mill, repair or replacement of the curtain protecting the expansion joint, repair or replacement of the divider plate separating the inlet and outlet, replacement or measurement of the ball charge, i.e. the 1 1/2 inch diameter balls in the mill, and repair or replacement of the mill head and barrel liners. The new design accomplishes its goals without jeopardizing the structural integrity of the mill end. An advantage is that the divider plate can be removed or installed as one piece, without cutting it into multi-pieces, by bolting it in place. With the prior design, the divider plate had to be cut into four pieces and welded internally in the mill. The present access and removal features also improve the ability of maintenance personnel to access the inlet and outlet ducts. The present design results in significant cost savings in maintenance, man hours and downtime.